Dual-Torque Orthopedic Set Screw Driver for Spinal Rod Fixation
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Solution Overview
Problem
Existing orthopedic tools face challenges in determining the right amount of torque to apply to set screws during spinal surgery, which can lead to issues like screw loosening and implant breakage.
Innovation Solution
The implementation of a dual-torque limiting mechanism in a set screw driver that applies a first torque level for initial attachment and a higher second torque level for final fixation, with optional tactile and auditory feedback to indicate torque levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single torque level is applied to the set screw, then the device structure remains simple, but the reliability of the rod-to-screw attachment is compromised due to insufficient torque control
Solution Approach 1:
The torque control mechanism is segmented into two distinct torque limiting mechanisms: a first torque limiting mechanism that limits torque to a first level (e.g., for initial rod reduction), and a second torque limiting mechanism that limits torque to a second level (e.g., for final set screw tightening). This segmentation allows each mechanism to be optimized for its specific torque level, improving overall reliability while keeping each individual mechanism relatively simple.
Solution Approach 2:
The first torque limiting mechanism is engaged initially to perform preliminary actions (rod reduction, initial attachment) at a lower torque level. After this preliminary action is complete, the first mechanism is disengaged and the second torque limiting mechanism is engaged for final tightening at a higher torque level. This preliminary action approach ensures that each torque level is applied at the appropriate stage of the procedure.
2Reliability
If torque application is not precisely controlled, then the surgical process remains simple and quick, but the risk of screw loosening and implant breakage increases
Solution Approach 1:
The torque limiting mechanisms provide mechanical feedback to the surgeon during the tightening process. When the predetermined torque level is reached, the limiting mechanism prevents further torque application, giving the surgeon immediate feedback that the appropriate torque has been applied. This feedback mechanism ensures precise torque control without requiring the surgeon to estimate or calculate the required torque.
Solution Approach 2:
The torque limiting mechanisms are designed to automatically limit torque at the predetermined levels without requiring external monitoring or adjustment by the surgeon. The mechanisms self-regulate the torque application, making the system self-service in terms of torque control. This reduces the cognitive load on the surgeon while ensuring reliable torque application.
3Strength
If higher torque is applied to ensure secure attachment, then the attachment strength improves, but the risk of implant breakage and screw loosening increases
Solution Approach 1:
The system changes the torque parameter in two distinct stages: first applying a lower torque level (first torque level) for initial attachment and rod reduction, then applying a higher torque level (second torque level) for final tightening. Each torque level is carefully selected and limited to prevent exceeding the damage threshold. This parameter change approach ensures that the attachment strength is sufficient while avoiding implant damage.
Solution Approach 2:
The torque limiting mechanisms act as a form of beforehand cushioning by preventing torque from exceeding the predetermined safe levels. The first torque limiting mechanism cushions against excessive torque during the initial attachment phase, and the second torque limiting mechanism cushions against excessive torque during final tightening. This prior cushioning protection ensures that implant damage is prevented before it can occur.
Data Source
Figure 1A
Figure 1B
Figure 1C~1E
AI summary
An orthopedic implant kit for tightening a set screw to a head of a pedicle screw for holding a spinal rod to the pedicle screw, the kit including a screw extender for holding the head of the pedicle screw, a set screw driver for engaging with the set screw to threadably tighten the set screw to the head of the pedicle screw, a first torque limiting mechanism for limiting a torque between the set screw driver and the screw extender to a first torque value or a first torque indication mechanism for indicating that the first torque has been reached, and a second torque limiting mechanism for limiting a torque between the set screw driver and the screw extender to a second torque value, the second torque value being higher than the first torque value.